86 



Basic Structure of Vertebrates 



NEPHROGENIC TISSUE 



GLOMERULI 



Fig. 84. A diagram illustrating the repeated branching of the collecting tubules 

 in a nine-week (30 mm.) human embryo. Roman numerals indicate successive 

 branchings. The diagram shows also the origin of excretory tubules from the 

 nephrogenic tissue. (Redrawn from Braus, after Kampmeier. (Courtesy, Neal and 

 Rand: "Chordate Anatomy," Philadelphia, The Rlakiston Company.) 



Proximal convoluted tubule 



Fig. 85. Diagrams of the finer structure of a mammalian kidney. {Left) A sec- 

 tion of the entire kidney showing the contrast between cortical and medullary 

 regions. The relations of the chief arteries and veins are indicated. {Right) A recon- 

 struction of a single excretory tubule, showing its relation to the glomerulus, its 

 differentiation into a proximal convoluted region, loop of Henle, and a distal 

 convoluted region whence it emerges from the cortex and passes on into one of the 

 collecting tubules of the medulla. The relations of blood-vessels to the excretory 

 structures are shown. 



